Ladder frames as support for the paneling of a motor vehicle body have been known for more than a hundred years. Modern self-supporting passenger car bodies frequently include an understructure with side members and cross members which, even if these merely have to absorb a part of the static forces that occur on a motor vehicle, can be considered a ladder frame.
Such an understructure is known from U.S. Pat. No. 6,540,286 B2. The understructure includes two side members, which extend over the entire length of the vehicle and are interconnected by multiple cross members of a cross section that is constant over their length. In that these cross members are cut to size from a prefabricated cylindrical tube in the respective length required, bodies can be produced in different width. Some of these cross members abut lateral flanks of the side members located opposite one another, while others laterally protrude over the side member and are therefore fastened supported by these side members. The small size of the contact area between the side members and cross members contacting or crossing one another exacerbates the production of a connection that can be subjected to torsional load.
In the case of the cross member abutting the side members, the cross members have to maintain a predetermined length with high precision in order to ensure that all cross members can be welded together with an adequately uniform gap width between them and the side members. The production of the cross members in an exactly predetermined length is rendered substantially more difficult when the area of the side member, to which the cross members have to be welded, is not flat. This restriction in turn is disadvantageous for the load capacity of the weld.
There is therefore a need for a motor vehicle understructure that can be produced efficiently and with a small number of different parts yet achieves a high load capacity with low weight.